Browsing by Author "Martin A. Hubbe, Committee Member"

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Adsorption of Amphoteric and Nonionic Polymers on Model Thin Films
(2008-08-19) Song, Junlong; Kirill Efimenko, Committee Member; Dimitris S. Argyropoulos, Committee Member; Martin A. Hubbe, Committee Member; Orlando J. Rojas, Committee Chair
Understanding the adsorption behaviors of polymers from solution is critical in applications such as fiber processing, specifically in the development of fiber bonding and lubrication. Therefore, in situ and real time Quartz Crystal Microbalance and Surface Plasmon Resonance were employed to monitor the adsorption of hydrosoluble polymers (including amphoteric and nonionic macromolecules) on ultrathin films of cellulose, polypropylene, polyethylene, nylon and polyethylene terephthalate (typical paper and textile materials). The extent of adsorption of amphoteric polymers on cellulose (and also on silica) depended on the charge density of the substrate and pH of the medium. More importantly, the adsorbed amount exceeded that found in the case of simple polyelectrolytes. We hypothesized that this extensive adsorption is the result of a polarization effect produced by the charged substrate, which also determined the characteristics (thickness and viscoelastivcity) of the adsorbed layers as well as bonding abilities. Surface active polymers including diblock polyalkylene glycols and triblock polymers (based on ethylene- and propylene- oxide) as well as silicone surfactants were used to study the formation of boundary layers that are relevant in fiber lubrication. Adsorption isotherms for the nonionic polymers followed a Langmuirian behavior in which the hydrophobic effect was a major driving mechanism. The molecular mass of the polymer influenced markedly adsorption and, compared to typical hydrocarbon surfactants, silicone-based surfactants showed a higher surface activity and affinity with the tested hydrophobic surfaces. Lateral force microscopy and molecular dynamics simulation were used to illustrate boundary lubrication. It was concluded that surface-active molecules form robust self assembled (lubricant) layers that withstand high shear forces and are able to control friction and abrasion due to the unique molecular structures they form at the interface. Overall, it is anticipated that this thesis will contribute to the elucidation of the relationship between the structure and chemical nature of the adsorbing polymers and their respective interfacial behaviors.
An Atomic Force Microscopy Study of the Local Hygro-expansion Behavior of Cellulose Microfibrils
(2007-03-01) Lee, Jung Myoung; Joel J. Pawlak, Committee Chair; John A. Heitmann, Committee Co-Chair; Martin A. Hubbe, Committee Member; Dimitris S. Argyropoulos, Committee Member
Structure-property relationships of cellulose-based materials including paper, micro- and nano-fiber composites are often strongly influenced by environmental variables. The interaction of polymeric and crystalline structure in cellulose bio-based materials is of high technological importance. Therefore, understanding the underlying mechanism of environmental/material interactions is crucial for engineering products from bio-based materials. This study was undertaken in an effort to develop a technique for the assessment of dimensional stability of cellulose microfibrils as a function of different relative humidity. Analysis of atomic force microscopy images showed that the local dimensional properties of cellulose microfibrils are highly responsive to variable relative humidity, and their hygro-expansive behavior depends on the relative humidity history, and their method of preparation. The results obtained suggested that dimensional and hygro-expansive behaviors of cellulose microfibrils are related to their ultra-structural arrangements and their origin, either directly or indirectly. These findings, hopefully, will prompt an open discussion regarding the dynamic interactions between cellulose and water molecules at a nano-scale.
Behavior of Adhesive Materials in Screening Devices for Paper Recycling
(2004-04-28) Lucas, Bradley Earle; Hasan Jameel, Committee Co-Chair; Martin A. Hubbe, Committee Member; Saad A. Khan, Committee Member; Richard A. Venditti, Committee Co-Chair
The objective of this research is to understand the behavior of pressure sensitive adhesive (PSA) materials in industrial and laboratory screening devices. The research was initiated by screening pulp containing PSA using an industrial pressure screen with fine slots. The industrial pressure screen removed less than 80% of the feed PSA contaminant. In contrast, an atmospheric laboratory screen of the same slot width, 0.006 inches, removed 99% of the PSA. One of the reasons for the lower removal efficiency was found to be a significant breakage of PSA particles into smaller particles within the industrial pressure screen. The breakage of PSA particles in a shear field was studied using a high shear mixer and the consistency was found to be the most significant variable affecting the breakage of the PSA. It was also of interest to investigate how the PSA material could deform and pass through the fine slot of a pressurized industrial screen. A laboratory screening device with a single slot was developed to study the passage of PSA particles through the slot as a function of pressure drop across the slot. It was observed that at moderate pressure drops, particles with their smallest dimension up to five times the slot width passed through the slot. Increased temperature promoted the passage of the particles through the slot, indicating that the physical properties of the PSA influenced its passage. To understand the relationship between PSA formulation, physical properties, and passage of particles through a fine slot, several PSA formulations of known composition were prepared for analysis. Differences in the PSA formulations were found to affect the yield strain, yield stress, and modulus of the PSA films, which correlated with particle breakage in the pulper. Yield stress and particle area correlated with particle passage through the slot. A mechanical model for passage is in agreement with the experimental results, indicating that yield stress and particle size are significant for PSA particle passage through fine slots. These studies have resulted in important information for screen manufacturers, paper recyclers, and PSA producers to improve the removal of PSA particles from recovered paper.
The Effects of Water to Stucco Ratio and Additives on Gypsum Crystal Morphology and Adhesive Forces
(2008-07-05) Austin, Kathryn M.; Martin A. Hubbe, Committee Member; John A Heitmann, Committee Member; Joel J. Pawlak, Committee Chair
Structure-Process-Property Relationships in Elastic Nonwovens Made From Multi-Block Elastomers
(2008-03-10) Begenir, Asli; Stephen Michielsen, Committee Co-Chair; Behnam Pourdeyhimi, Committee Co-Chair; Sam M. Hudson, Committee Member; Martin A. Hubbe, Committee Member
Melt-blown webs from ester and ether thermoplastic polyurethanes (TPU) and polyether-block-amide (PEBA) elastomers were produced at different die-to-collector distances (DCD) to study the correlation between polymer type, process conditions and web properties. Air temperature and velocity profiles were measured and modeled to correlate fiber formation to melt-blowing conditions. Isothermal crystallization kinetics was measured by DSC, and analyzed by traditional Avrami and model proposed by Kurajica. Web tensile properties were explained in terms of crystallization kinetics along with air temperature profile. Crystallization kinetic parameters derived from both models exhibited similar temperature, polymer type and hardness dependence. The air flow field from simulations showed good agreement with experimental profiles and enabled modeling of fiber formation in melt-blowing. Both air temperature and velocities dropped significantly even at the die tip and continued to fall rapidly until reaching a plateau. The crystallization onset temperatures were found to fall within DCD region of rapid air velocity and temperature drop. This suggests that polymers already started to crystallize before collector, the extent of which depends on crystallization kinetics. Web strength behavior was highly dependent on DCD and polymer hardness. By mapping crystallization behavior onto air temperature profile, polymer crystallization kinetics was observed to have a profound effect on web strength. This was clearly demonstrated in PEBA series, in particular with the hardest grade, P55 which produced the lowest web strength mainly due to its significantly higher crystallization rate. It is concluded that web tensile behavior is strongly dependent on degree of fiber solidification achieved within the web, which is determined by crystallization kinetics and distances traveled between die and collector. Moreover, polymer extrusion and air temperatures as well as air velocity are critical in determining the amount of time it takes for polymer melt to travel the distance from the die to collector and the temperature that fibers have upon reaching collector.